1. Field of the Invention
The present invention relates to optical devices and methods for producing and operating them. Particularly, the present invention relates to optical resonators and their applications in tunable semiconductor lasers.
2. Description of the Related Art
In recent years, the development of optical devices for various applications such as tunable semiconductor lasers has received much attention. For example, fiber optic communication systems employ widely tunable semiconductor lasers in wavelength division multiplexing applications. Accordingly, various forms of tunable semiconductor lasers and related devices have been developed.
Many of the developed tunable semiconductor lasers require relatively complex manufacturing processes and may employ grating structures and/or moving components. In addition, multiple optical couplers in many tunable semiconductor lasers can reduce the overall performance, such as indicated by the mode suppression ration (MSR).
Two fundamental types of optical resonators are the Fabry-Perot cavity and the ring resonator. The Fabry-Perot cavity comprise two parallel reflective planes separated by a distance. Resonance (constructive interference of the reflected light) occurs for specific wavelengths of light reflected between the reflective planes when the distance between the planes is an even multiple of the light wavelength. Thus, the pattern for resonance is periodic across wavelengths. Reflective gratings have also been used in the place of the reflective planes achieve similar results. In addition, ring resonators establish resonance in a similar manner, but the critical distance is defined by the circumference of circular waveguide rather than the separation between two reflective planes. Both fundamental types of optical resonators have been used in a vast number of various optical devices such as tunable lasers. However, both types present different manufacturing and design difficulties in their use. For example, conventional Fabry-Perot resonators are typically constrained (or are constrained by) other device parameters, e.g., the gain medium length must coincide with the length of the Fabry-Perot cavity. The use of ring resonators is often complicated by the need for multiple coupling regions.
There is a need for optical resonators which are simple to manufacture and can be used in the production of optical devices such as tunable semiconductor lasers. Further, there is a need for optical resonators which can be implemented with fewer manufacturing and design constraints. There is also a need for tunable semiconductor lasers which operate without grating structures or moving components. As detailed hereafter, the present invention possesses these and other advantages.